1. Field of the Invention
The present invention relates to an apparatus which controls driving of an optical apparatus such as a zoom lens apparatus used for a TV camera and video camera.
2. Description of the Related Art
In a front-focus system in which a focus lens unit is placed closer to an object side than a magnification-varying lens unit, an amount of movement of a lens barrel does not change when magnification is varied, and therefore the front-focus system is advantageous for a manual focusing system. Thus, the front-focus system is widely used for broadcasting zoom lenses in which primary importance is attached to manual operation and for commercial use zoom lenses.
On the other hand, a rear-focus system in which a focus lens unit is placed closer to an image side (image-taking apparatus side) than a magnification-varying lens unit is advantageous in reducing the size and weight of the focus lens unit, and therefore the rear-focus system is widely used for a zoom lens apparatus with an auto focusing system.
With increasing diversification of camerapersons and image-taking conditions of a zoom lens apparatus for a TV camera in recent years, there is a demand for enhanced operability and maneuverability, and therefore there is a rising demand for equipment provided with both manual focusing (hereinafter referred to as “MF”) and auto focusing (hereinafter referred to as “AF”).
Furthermore, the zoom lens apparatus proposed in Japanese Patent No. 2561637 and Japanese Utility Model Publication No. S62(1987)-43286 uses a lens unit for AF placed closer to an image side than a magnification-varying lens unit and uses a lens unit for MF placed closer to an object side than the magnification-varying lens unit, thus providing an AF/MF switchable zoom lens.
The above described AF/MF switchable zoom lens is constructed of, in order from the object side, a first focus lens unit for manual focusing, a magnification-varying lens unit which moves on the optical axis to vary magnification, a correction lens unit for correcting the image plane which varies due to the change of magnification and a relay lens unit which contributes to image formation on an image-pickup device such as a CCD sensor or a C-MOS sensor. Furthermore, a second focus lens unit for auto focusing is placed in the relay lens unit.
During an MF mode operation, the second focus lens unit is fixed at a predetermined position and focusing is carried out by manually operating the first focus lens unit.
Then, when the MF mode is switched to the AF mode, the first focus lens unit is fixed at the position where the switching is performed and auto focusing is carried out by driving the second focus lens unit by a motor. Then, when the AF mode is switched to the MF mode, the second focus lens unit is automatically returned to the abovedescribed predetermined position and fixed in conjunction with the switching.
However, when the AF mode is switched to the MF mode, if, for example, the first focus lens unit is fixed at infinity, while the second focus lens unit which has been under AF control on the object at a finite distance is automatically returned to a predetermined position other than infinity, defocusing occurs.
This defocusing can be generally solved by operating the first focus lens unit in such a way that an in-focus position is manually found on the telephoto side. However, when an image is taken on the wide-angle side, if the AF mode is switched to the MF mode, the cameraperson must carry out a zooming operation up to the telephoto side first and then manually carry out focusing operation.